The ability to redirect cellular processes from proliferation to terminal differentiation offers a promising approach toward preventing cancer progression, and understanding the molecular mechanisms involved in this switch can potentially uncover important targets for early detection of cancer. We have been studying differentiation in non-small cell lung cancer cell lines by three different approaches: 1) Develop model systems of differentiation to enable the study of molecular mechanisms of differentiation control in lung carcinogenesis. We have identified new model systems of terminal and reversible epithelial differentiation. Treatment of the NSCLC cell line H358 with the tumor promoter mezerein and the cell cycle inhibitor aphidicolin results in striking morphologic changes, cell cycle arrest, growth inhibition, and alteration in mucin expression. Current studies are examining the relationship between cell cycle control and differentiation. 2) Study differentiation markers and genes controlling differentiation and proliferation in primary lung tumors, premalignant lesions, and cell lines to identify targets for early detection screening. We have shown that cJun, a known mediator of tumor promotion, is rarely expressed in normal pulmonary epithelium, but 50-90% of atypical/premalignant lesions express cJun. Expression is lower in primary tumors, but cell line analysis reveals that cJun is functional and capable of mediating growth factor signals even under in vitro conditions. These results suggest a role for cJun in early carcinogenesis and a potential role as a target for early detection of lung cancer. Studies are being broadened to include premalignant lesions of the esophagus and a hamster carcinogenesis model. 3) Evaluating the function and regulation of the Clara cell protein CC10. Transgenic mouse model systems suggest that CC10 expression is lost early during lung carcinogenesis and CC10 mRNA is absent by Northern analysis in 8/10 NSCLC cell lines. We showed that overexpression of CC10 results in decreased clonogenic survival, decreased invasiveness, and decreased expression of metalloproteases, suggesting that downregulation of CC10 contributes to neoplastic progression. These studies will shed light on the biology of lung cancer and enable us to identify targets for early detection and intervention as well as potentially develop strategies for enforcing terminal differentiation as a therapeutic goal during lung carcinogenesis.